Takehiro Ozawa, Shinichi Ishiwata, Yoshihisa Kano
For blends of acrylate copolymer [poly(2-ethyl hexyl acrylate-co-acrylic acid) ; P(2EHA-AA)] with ultraviolet (UV) curable oligomer [urethane acrylate oligomer ; UAO], pressure-sensitive adhesive (PSA) properties, such as peel adhesion, probe tack, and holding power were examined. The values of peel adhesion and probe tack of the P(2EHA-AA) / UAO blends were dramatically reduced by UV irradiation. However, all blends had a high holding power even when cured by UV irradiation. The mechanism of reduced PSA properties was investigated via dynamic mechanical properties, DSC, and dynamic contact angle DCA. Peel adhesion decreased monotonically with an increase of storage moduli E' and loss moduli E" for all non-UV and UV cured blends. Since moduli values and glass transition temperatures Tg of these blends after UV irradiation were higher than those of these blends before UV irradiation, we judged that reduced peel adhesion and probe tack values were caused by the moduli increase and the Tg increase due to UV irradiation. In other words, the deformation energy of UV cured blends when conducting adhesive tests was reduced by the curing process. The DCA values of non-UV cured blends were same as those of UV cured blends. We presumed that the segment mobility of polymer chains on the surface did not influence the reduced peel adhesion and probe tack values.